This invention relates generally to the refrigeration and preferably liquefaction of industrial gas and is particularly useful for bringing the gas from ambient temperature to a cryogenic temperature to effect the refrigeration.
The refrigeration of industrial gases is an important step which is used in many industrial operations. Typically the industrial gas is refrigerated and optionally liquefied by indirect heat exchange with a refrigerant. Such a system, while working well for providing refrigeration over a relatively small temperature range from ambient, is not as efficient when refrigeration over a large temperature range, such as from ambient to a cryogenic temperature, is required. One way this inefficiency has been addressed is to use a refrigeration scheme with multiple circuits wherein each circuit serves to reduce the temperature of the industrial gas until the requisite temperature is reached. However, such multiple circuit industrial gas refrigerators may be complicated to operate.
A conventional single circuit refrigerator or liquefier system is much less complicated than a multiple circuit refrigerator liquefier but such a system imposes very stringent requirements on the selection of the refrigerant. A recent significant advancement in the field of industrial gas liquefaction is the use of a multicomponent refrigerant fluid instead of the single component refrigerant conventionally used in cooling or liquefying circuits. However, even with the use of a multicomponent refrigerant fluid in a single circuit system, it is costly to carry out the cooling over a large temperature range, such as from ambient temperature to a cryogenic temperature as would be necessary for the liquefaction of an industrial gas, because of the equipment and process steps needed to ensure that one or more components of the refrigerant or other matter such as equipment lubricant does not freeze at the lower temperatures.
Accordingly, it is an object of this invention to provide an improved system for refrigerating an industrial gas, which employs a multicomponent refrigerant fluid.
The above and other objects, which will become apparent to those skilled in the art upon a reading of this disclosure, are attained by the present invention, one aspect of which is:
An industrial gas refrigerator comprising:
(A) A multistage heat exchanger comprising an initial stage and a final stage;
(B) means for passing industrial gas through the multistage heat exchanger, and means for recovering refrigerated industrial gas from the final stage of the multistage heat exchanger;
(C) means for passing multicomponent refrigerant fluid through the initial stage of the multistage heat exchanger;
(D) a phase separation device having a vapor exit, and means for passing multicomponent refrigerant fluid from the initial stage of the multistage heat exchanger to the phase separation device; and
(E) means for withdrawing multicomponent refrigerant fluid from the vapor exit of the phase separation device, and means for passing essentially all of the fluid withdrawn from said vapor exit of the phase separation device to the final stage of the multistage heat exchanger.
Another aspect of the invention is:
A method for refrigerating industrial gas comprising:
(A) providing a multistage heat exchanger comprising an initial stage and a final stage;
(B) passing multicomponent refrigerant fluid through the initial stage of the multistage heat exchanger and withdrawing multicomponent refrigerant fluid in both a vapor phase and a liquid phase from the initial stage of the multistage heat exchanger;
(C) passing the multicomponent refrigerant fluid withdrawn from the initial stage of the multistage heat exchanger to a phase separation device having a vapor exit;
(D) withdrawing multicomponent refrigerant fluid from the vapor exit of the phase separation device and passing essentially all of the fluid withdrawn from the vapor exit of the phase separation device to the final stage of the multistage heat exchanger; and
(E) passing industrial gas through the multistage heat exchanger and recovering refrigerated industrial gas from the final stage of the multistage heat exchanger.
As used herein the term xe2x80x9csubcoolingxe2x80x9d means cooling a liquid to be at a temperature lower than saturation temperature of that liquid for the existing pressure.
As used herein the term xe2x80x9cnormal boiling pointxe2x80x9d means the boiling temperature at 1 standard atmosphere pressure, i.e. 14.696 pounds per square inch absolute.
As used herein the term xe2x80x9cindirect heat exchangexe2x80x9d means the bringing of fluids into heat exchange relation without any physical contact or intermixing of the fluids with each other.
As used herein the term xe2x80x9cexpansionxe2x80x9d means to effect a reduction in pressure.
As used herein the terms xe2x80x9cturboexpansionxe2x80x9d and xe2x80x9cturboexpanderxe2x80x9d means respectively method and apparatus for the flow of high pressure fluid through a turbine to reduce the pressure and the temperature of the fluid thereby generating refrigeration.
As used herein the term xe2x80x9cvariable load refrigerantxe2x80x9d means a mixture of two or more components in proportions such that the liquid phase of those components undergoes a continuous and increasing temperature change between the bubble point and the dew point of the mixture. The bubble point of the mixture is the temperature, at a given pressure, wherein the mixture is all in the liquid phase but addition of heat will initiate formation of a vapor phase in equilibrium with the liquid phase. The dew point of the mixture is the temperature, at a given pressure, wherein the mixture is all in the vapor phase but extraction of heat will initiate formation of a liquid phase in equilibrium with the vapor phase. Hence, the temperature region between the bubble point and the dew point of the mixture is the region wherein both liquid and vapor phases coexist in equilibrium. In the practice of this invention the temperature differences between the bubble point and the dew point for the variable load refrigerant is at least 10xc2x0 K., preferably at least 20xc2x0 K. and most preferably at least 50xc2x0 K.
As used herein the term xe2x80x9cindustrial gasxe2x80x9d means a fluid having a normal boiling point of 150xc2x0 K. or less. Examples of industrial gases include nitrogen, oxygen, argon, hydrogen, helium, carbon dioxide, carbon monoxide, methane and fluid mixtures containing one or more thereof.
As used herein the term xe2x80x9ccryogenic temperaturexe2x80x9d means a temperature of 150xc2x0 K. or less.
As used herein the term xe2x80x9crefrigerationxe2x80x9d means the capability to reject heat from a subambient temperature system to the surrounding atmosphere.
As used herein the term xe2x80x9catmospheric gasxe2x80x9d means one of the following: nitrogen, argon, krypton, xenon, neon, carbon dioxide, oxygen and helium.
As used herein the term xe2x80x9creflux columnxe2x80x9d means a separation device which allows for the countercurrent flow of upwardly flowing vapor against downwardly flowing liquid whereby heavier components in the vapor are washed out of the vapor into the liquid, and the downflowing liquid, or reflux, is produced by partially condensing the vapor at the top of the column. In this way the vapor exiting the top of the column is richer in the lighter components of the feed into the column and the liquid exiting the bottom of the column is richer in the heavier components of the feed into the column.